1. Field of the Invention
The present invention is directed to a photosensitive matrix device having a substrate upon which strip-like row conductors and strip-like column conductors are arranged to form a plurality of points of intersection with a photoconductive cell arranged in series with a rectifier at each point of intersection for connecting the row conductor to the column conductor.
2. Prior Art
A photoconductive cell matrix assembly, which has a substrate provided with a plurality of row conductors and a plurality of column conductors intersecting the row conductors at points of intersection, and the intersecting conductors are separated by insulation at the point of intersection and interconnected by a photoconductive cell arranged adjacent each point of intersection, is disclosed in U.S. Pat. No. 3,900,883, which corresponds to German Offenlegungsschrift 2,349,233. This photoconductive matrix is preferably used as a punch card reader, wherein light striking a photoconductive cell causes the cell to allow a flow of current from one conductor to the other conductor to produce a signal.
Other types of photoconductive cell matrices for use in a card reader are disclosed in copending United States patent application Ser. No. 580,919, filed May 27, 1975, which issued as U.S. Pat. No. 4,020,474 and corresponds to German Offenlegungsschrift 24 25 467. In this application, each photoconductive cell is arranged in series with a rectifier so that current flow is limited to one direction.
Known punch card readers often create false signals. The false signals may be due to the fact that when light is projected through a hole in the punch card onto a particular matrix dot or cell, adjacent dots or cells which are positioned under points of the punch card which do not contain holes still receive sufficient light to allow current flow between the conductors and create a false signal. In the past to prevent these interferring signals or cross talk between adjacent cells, it has been suggested to use a number of partially expensive and time-consuming measures to optically insulate each cell from adjacent cells. For instance, one suggested method of eliminating the false signals is to form light channels directly ahead of each of the individual matrix elements and to simultaneously illuminate the card with a bundle of light beams which extend as parallel as possible so that light passing through an opening in the card does not diverge out of the area of the cell for the particular opening. However, the optical insulation of the individual cells of light-sensitive matrix of cells was still not perfect in many instances.